Nalby, you could probably lean it out a bit more if you want, but try out the larger pitch prop and see how it goes. Running it rich is likely not to hurt it, but with 20:1 oil ratio, it might start getting some carbon build up if you are always rich. 5mins warming up is not necessary I dont think, you would be ok with starting it up, getting it onto a high idle, after a minute, rev it up a few times, and make sure it is firing on all cylinders, and then get her up in the air. Excessive idling also causes carbon build up...
Smotherb, get the timing ring done as a priority. Retune it with the new timing ring and go fly. I have no experience with the roto-flow tanks, so cannot comment on their viability in this application, but go over your tank/tubing install and check the plumbing for any abnormalities. I use a standard setup with a heavy felt clunk and hav never experienced any inverted problems involving cutting out. Although these carbs ARE pumped, I dont think that the pump is as effective as a walbro type setup so if your tank is far away there is a possibility the pump isnt able to overcome the distance. My experience with the carbs is that they are pretty effective in keeping a decent flow of fuel so make sure that any possible resistance is minimised. Some people put inline filters in and if the roto is offering any resistance to flow....it will cause this. I have just had a look at the rotoflow and some reviews and it seems good, but I cannot help thinkin that with the rotating part and all the o-rings, there is more of a chance with something going wrong than with just a normal clunk setup...just an opinion, but sometimes K.I.S.S (Keep it simple, stupid) applies. if it persists, then try a normal tank set up and see if it helps.
The fuel consumption on these engines is so low that its not like they need MASSIVE fuel flow, so its a bit weird you are having these problems....maybe back to baiscs and see how it goes.
but......get that timing sorted out, if you think the engine is running well now, wait until you get the timing right....